Fibrous proteins Collagen, Keratin and Elastin

https://www.youtube.com/watch?v=oZpt1Pcx-OU

What role do fibrous proteins play

A structural role, e.g in bones or tendons, or in the walls of blood vessels such as arteries.

Fibrous proteins tend to form long, rope-like molecules.

They also have a large proportion of amino acids with hydrophobic R group, fibrous proteins are insoluble in water

Where is collagen found

In tendons, which connect muscles to bones and in ligaments which connect bones to each other.

Also found in skin

Key feature of collagen that its a strong molecule, this is due to its structure

Structure of collagen

Polypeptide chains in collagen wrap tightly together to form a triple helix

In collagen polypeptides, every third amino acid is glycine, R group of glycine is hydrogen atom, this means glycine has smallest R group, allowing collagen polypeptides to wrap very tightly around each other.

As they wrap around, large number of hydrogen bonds form between polypeptide chains. they help to stabilise quaternary structure of protein.

Collagen is further strenghtened by crosslinking between different triple helical molecules

What is keratin

A fibrous protein which is found in hair, fingernails and outer surface of skin.

It is very strong and insoluble in water.

What does keratin consist of

Long stranded molecules, also contains a high proportion of amino acid cysteine. Cysteine is used to form disulfide bonds, this causes keratin molecules to contain large number of disulfide bonds, contributing to strength of keratin.

What is elastin

A fibrous protein. The skin contains a large amount of elastin fibres, helps to make skin elastic

They are long strands involving hydrophobic region, the strands are also cross linked to each other.

When stretched, the strands move apart, but remain attached to crosslinks, and after stretching the elastin molecules, they reassociate and spring back together.